1. Field of the Invention
The present invention relates to an ion implanting apparatus and an ion implanting method using the same. More specifically, the present invention is directed to an ion implanting apparatus that is capable of real-time charge monitoring system, the apparatus having an improved signal/noise ratio, and an ion implanting method using the same.
2. Description of the Related Art
In an ion implantation process, specific ions are doped to form a conductive region having a desired conduction type. In the semiconductor industry, ion implantation has been widely used to precisely form a thin region having a desired impurity concentration on a wafer. Since ions are charged particles, a workpiece implanted with the ions has the same charge as the ions. Because implanted ions have an energy on the order of several KeV to hundreds of KeV, secondary electrons may be discharged from the ion-implanted workpiece. Thus, ion implantation causes charges to accumulate on an insulator or a conductor.
A semiconductor wafer used to manufacture a semiconductor device includes an insulator, such as a gate oxide, and a conductor, such as a gate electrode. In a metal-insulator-semiconductor (MIS) structure, a capacitance (C) is made and a voltage (V) corresponding to charge quantity (Q)/capacitance (C) is generated, i.e., V=Q/C. For example, if cations are implanted into a wafer, numerous cations are accumulated on a conductor (e.g., the gate electrode) formed over an insulator (e.g., the gate oxide) to generate a voltage crossing an MIS capacitor formed of the conductor (gate electrode), the insulator (gate oxide), and the semiconductor (wafer). This voltage may lead to breakdown of the insulator. A breakdown of the insulator invites breakage of an LSI pattern of DRAM or flash memory series and results in a decrease in LSI manufacturing yield.
To protect a wafer from damage caused by charge accumulation (charge-up), a quantity of charges is reduced or charges of opposite polarity are used to neutralize the charges. Generally, ion implantation uses cations created by separating electrons from atoms. If electrons are coupled to cations, positive charges of the cations are neutralized. Conventionally, an electron shower has been used as an electron source for providing electrons to a wafer being ion-implanted to neutralize position ions.
FIG. 1 illustrates a cross-sectional view of a conventional ion implanting apparatus. FIGS. 2 and 3 are graphs for explaining disadvantageous aspects of the conventional ion implanting apparatus shown in FIG. 1.
In an ion implantation using an electron shower, it is desirable to continuously monitor the charge-up of the wafers being ion-implanted and to control the neutralization to minimize the charge on the wafers. Referring to FIG. 1, a first conductor 41 is positioned on a front surface of a disk 31, a second conductor 43 is positioned on a rear surface of the disk 31, and a third conductor 47 is fixed to a chamber 15. Charges accumulated on the first conductor 41 migrate through the second and third conductors 43 and 47 to detect a charged state of the wafer 35.
A procedure of transmitting a charge voltage applied to the second conductor 43 to the third conductor 47 is induction of capacitive coupling. Capacitance is inversely proportional to a distance between a measured face and a probe, and an output signal of a sensor is dependent on the capacitance. Therefore, as a distance between the second and third conductors 43 and 47 increases, an output signal from the third conductor 47 being a sensor decreases, as shown in FIG. 2. As a result, an error based on distance is generated.
The first conductor 41 must detect only cations. The first conductor 41, however, is constructed to face an emitted ion beam, so that it detects not only cations but also anions, neutrons, and secondary electrons. Therefore, an unwanted peak, i.e., noise, is included in the output signal of the third conductor 47 by disturbance, as shown in FIG. 3. For this reason, a signal/noise (S/N) ratio is reduced.
As described above, the conventional ion implanting apparatus exhibits several disadvantageous features, such as the error based on a distance and the noise caused by disturbance, which impair reliability of detecting a charged state of a wafer surface. Therefore, an ion implanting process using the above-described conventional ion implanting apparatus cannot avoid impairment of detection reliability.